1. Field of the Invention
The present invention relates to the motorizing of wheeled conveyances and particularly to the provision of an electrical drive system which may be installed on existing manually powered wheelchairs or carts. More specifically, this invention is directed to a technique for adding an electromechanical drive to a wheelchair, and especially a conventional foldable chair, without impeding the ability to collapse the chair for vehicle transportation and/or storage. Accordingly, the general objects of the present invention are to provide novel and improved apparatus and methods of such character.
2 Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well suited for use in the conversion of conventional, foldable wheelchairs to motorized chairs. Most manually driven wheelchairs which are presently in use employ a dual-planar, tubular frame construction which has been available since the early 1940's. The motorized chairs which are commercially available are, for the most part, specifically designed for powered operation and cannot be folded. The inability to fold presents a problem for many disabled persons since it precludes the convenient transport of their motorized wheelchairs by car. Further, because of their uniquely designed frame construction, presently available motorized wheelchairs are comparatively costly and it must be noted that the added expense is greater than the cost of the motor(s) and related power supply and control circuitry.
It should be noted that, in order to remove the motors and power supply from a conventional motorized wheelchair in the interest of reducing weight and thereby enabling the lifting of the chair into a motor vehicle or aircraft, specialized tooling is customarily required and above-average mechanical skills are necessary. Also, further adding to the cost and complexity of presently available motorized wheelchairs, a mechanical release mechanism is required in order to disengage the motors thereby rendering it possible to push the chair manually.
Previous wheelchair motorized drive systems have taken a number of forms. Such systems may, for example, employ pinch rollers which contact the tires of the two large driven wheels of the chair in order to propel the chair. Among the disadvantages of the use of such pinch rollers are their inherent inefficiency, the uneven wheelchair tire wear they produce and the ever present danger of the user's hand becoming pinched between the roller and tire. Drive systems having motors that drive the wheels of a wheelchair via a chain mechanism or a friction belt are also available. In either case, the possibility is present for injury to the user because of the entanglement of clothing in the drive or the actual catching of a hand or finger in the drive.
U.S. Pat. Nos. 4,773,495 and 4,671,524 discuss drive mechanisms which are housed in the wheel hub of a wheelchair. U.S. Pat. No. 3,908,776 also discloses a special hub design for housing a drive mechanism. All of the prior hub mounted drive mechanisms are technically complex and require a special frame for the wheelchair. Thus, the mechanisms of the aforementioned patents cannot be employed to retrofit existing foldable wheelchairs.
U.S. Pat. Nos. 4,773,495 and 4,671,524 disclose rather elaborate means for disconnecting the motors from motorized wheelchairs in order to enable the transport of such chairs. In the patented drive systems power is transmitted from the motor shafts to the wheelchair wheels via a system of gearing and manual propulsion of the chair is not possible without interrupting the drive trains between the motors and wheels. U.S. Pat. No. 4,672,524 discloses another wheelchair drive wherein the driving means is located on a different axis from the driven wheel.
Many prior art motorized wheelchairs utilize friction drives. A friction drive for a wheelchair is exemplified by the disclosure of U.S. Pat. No. 4,037,676. The friction drive of U.S. Pat. No. 4,037,676 requires a special wheel which is provided with a friction drive surface on the inwardly facing surface of the rim. U.S. Pat. No. 4,424,873 discloses a friction drive which employs a belt to transmit power. All friction drives share the common deficiency of requiring constant maintenance. Other examples of the prior art relative to electric motor-driven wheelchairs may be seen from U.S. Pat. Nos. 3,770,073; 4,125,169; 4,512,613; 4,341,278; 4,421,336 and 4,115,670. The latter three of these patents all relate to control circuitry and command signal generators. Another electric wheelchair drive is depicted in U.S. Pat. No. 4,805,711 which is primarily related to the generation of command signals for the drive motors. U.S. Pat. No. 4,773,494 discloses a hydraulic drive for a wheelchair.